The invention relates generally to plasmonic materials and, more particularly, to a plasmonic interface between a plasmonic material and optical waveguide material and method for providing such an interface.
Plasmonic materials are materials that exploit surface plasmons, which are produced from the interaction of light with the plasmonic material, which according to various designs can be a metal-dielectric metamaterial or suitable metallic material (e.g., gold (Au) or silver (Ag)). Under specific conditions, the incident light couples with the surface plasmons to create self-sustaining, propagating electromagnetic waves known as surface plasmon polaritons (SPPs) or near-field light, which are much shorter in wavelength than the incident light.
One growing application of plasmonic materials is for use in plasmonic induced data storage. In plasmonic induced data storage, the near-field light generated by the plasmonic material—and the intense, localized optical fields of the near-field light—are focused and applied to a diffraction-limited spot over a small region of an optical disk containing metallic nano-structures to achieve high storage densities on the disk. One particular form of plasmonic induced data storage that continues to develop is heat assisted magnetic recording (HAMR), which is a technique that magnetically records data on high-stability media at a high storage density. In HAMR, a laser is used in conjunction with plasmonic materials to produce near-field light that momentarily heats the recording area of a recording medium to reduce its coercivity below that of a magnetic field applied from a recording head mechanism.
One known mechanism for generating near-field light is a near-field light generating device that includes a thin film optical light pipe or waveguide structure coupled to a thin film plasmonic material—with the thin film plasmonic material forming a structure that is commonly referred to as a near-field transducer (NFT). According to one embodiment, the optical light pipe/waveguide structure is formed of a waveguide material in combination with a buffer material—with one possible combination of the materials of the waveguide and the buffer layer being tantalum pentoxide (Ta2O5) as the material of the waveguide and aluminum oxide (Al2O3) as the material of the buffer layer. It is recognized, however, that the optical light pipe may be formed only of a waveguide material (e.g., Ta2O5) without the use of an accompanying buffer layer. Regarding the NFT, the plasmonic material of the NFT may be a noble metal such as Ag or Au.
A general construction of a material stack of a near-field light generating device as described above that includes a waveguide, a buffer layer, and a plasmonic material is shown in FIG. 1. As shown in FIG. 1, in the material stack 1 of the near-field light generating device, the construction is such that a thin film plasmonic material layer (forming an NFT) 2 is disposed on a thin film optical light pipe structure 3, with the thin film optical light pipe structure 3 being adhered to a supporting substrate layer 4 by way of an adhesive 5. The thin film optical light pipe structure 3 is formed of a waveguide layer 6 and a buffer layer 7, with the plasmonic material layer 2 being applied to the buffer layer 6 of the light pipe 3. In such a case, the material stack 1 is manufactured by forming the buffer layer 7 on the top surface of the waveguide layer 6, and forming the plasmonic material layer 2 on the buffer layer 7. It is recognized, however, that in the case of forming the plasmonic material layer 2 of a noble metal such as Ag or Au on the buffer layer 7 of Al2O3, there occurs the problem that the plasmonic material layer 2 may exfoliate in the process of manufacturing the material stack 1, since noble metals such as Ag and Au are low in strength of adhesion to Al2O3. To cope with this, an adhesion layer 8 made of metal, such as titanium, may be formed as an interlayer between the buffer layer 7 and the plasmonic material layer 2, with the adhesion layer 8 being deposited to adhere to the buffer layer 7 and promote the adhesion of the plasmonic material layer 2.
While the inclusion of the adhesion layer 8 in the above described material stack 1 of near-field light generating device provides for a strong adhesion between the plasmonic material layer 2 and the buffer layer 7 of the optical light pipe 3, the adhesion layer 8 can have a negative impact on the performance of the near-field light generating device in generating near-field light. That is, it is recognized that localized plasmon generation in the plasmonic material layer 2 and its efficiency in light energy conversion are both a function of the plasmonic material and the ability of applied light to efficiently couple into the plasmonic material. This efficiency in light energy conversion can be negatively affected by the presence of materials that reduce the ability of applied light to efficiently couple into the plasmonic material. With respect to the above described material stack 1, the titanium adhesive layer 8 results in such a loss of efficiency in light energy conversion, since the titanium adhesive layer 8 is applied directly between the optical light pipe 3 and the plasmonic material layer 2, and thus functions as a loss mechanism.
As an alternative method of forming a material stack of a near-field light generating device that includes a waveguide, a buffer layer, and a plasmonic material, it is recognized that a waveguide material could be sputtered onto a plasmonic layer to form the waveguide structure. However, it is recognized that such sputtering of the waveguide material will not provide a waveguide layer(s) that is stoichiometric, and thus a refractive index of the waveguide structure may not provide for optimal efficiency in the conversion of light energy into localized plasmon generation.
Therefore, it would be desirable to provide a material stack for a near-field light generating device that provides improved performance in generating near-field light, with the material stack providing optimal efficiency in the conversion of light energy into localized plasmon generation in the plasmonic material of the material stack. It would further be desirable for the material stack to maintain adequate adhesion between the thin film layers therein while providing this improved efficiency in light energy conversion, such that exfoliation of the plasmonic material from an optical waveguide is prevented.